The subject matter disclosed herein relates generally to imaging systems and techniques, and more particularly to energy spectrum analysis and gain adjustment.
In certain types of imaging devices, such as positron emission tomography (PET) scanners, arrays of detector elements are used to detect radiation emanating from the patient. In a PET scanner, for example, arrays of scintillator crystals may be used to detect annihilation photons which are generated inside the patient. The annihilation photons are produced when a positron emitted from a radiopharmaceutical injected into the patient collides with an electron causing an annihilation event. The scintillator crystals receive the annihilation photons and generate light photons in response to the annihilation photons, with the light photons detected by a photosensor configured to convert the light energy from the light photons to electrical energy used to reconstruct an image.
Detector behavior (e.g., detector gain), however, may vary over time. Detector gain depends, among other things, on the temperature of various components as well as a bias voltage applied to a silicon photomultiplier (SiPM). As the detector gain varies, the energy peak for detected events varies, reducing accuracy. Conventionally, peak stability as a function of temperature may be controlled using a thermal monitoring system, and used to adjust the gain based on the temperature. Such approaches work to an extent, but may not provide a desired level of peak stability or accuracy of gain adjustment. Peak instability may be a particular concern in PET systems used in conjunction with magnetic resonance imaging (MRI), as activation of gradient coils of an MRI system may result in relatively larger and/or quick increases in temperature.